> On Tue, Nov 30, 2010 at 11:59:57PM -0800, Tom Perrine spake thusly: >> (This is why HP and some other blade chassis actually shut down extra >> power supplies when the internal load is low, it is better to run >> fewer supplies are closer to 90-100% of their max, than to run more >> supplies at 20-30% of the rated loads.) > That is surprising to me. I thought running a power supply at 90-100% load > would result in the faster failure of the power supply? Especially since they > are nearly all over-rated. Maybe this is only good advice for properly > constructed HP blade chassis power supplies and not for typical servers. > > Anyone have any opinions on PSUs with power factor correction (PFC)? > > Yes, you want it. Think of the power factor correction as the percentage of usable work vs wasted energy. if your power factor is 90%, you need to oversize your UPS by 10% of the power draw on the machine because it's sampling more energy, more likely at peaks of the sine wave, vs. averaging sampling over the wave form. This results in current discontinuities in delivery and presents more load to the UPS and transformers.
I remember an old Best UPS in a job years ago that would graph the output current load and it looked like a peaked saw wave instead of a sine wave because of power supplies, at the time, that had about a .8 power factor. _______________________________________________ Tech mailing list [email protected] https://lists.lopsa.org/cgi-bin/mailman/listinfo/tech This list provided by the League of Professional System Administrators http://lopsa.org/
